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Biomedical subjects

C Y Chan

Publications and source records attributed to C Y Chan.

At least 145 records · Page 8Linked to original sources
PubMed1990

Heat probe thermocoagulation as a substitute for surgical intervention to arrest massive peptic ulcer hemorrhage: an experience in 153 cases.

In a period of 2 years 7 months, we performed heat probe (HP) thermocoagulation in 153 cases of massive peptic ulcer hemorrhage. The male/female sex ratio was 125/28. The average age was 57.6 +/- 1.3 years (mean +/- SEM; range, 17 to 88). There were 69 cases (45.1%) of spurting hemorrhage, 50 cases (32.7%) of oozing hemorrhage, and 34 cases (22.2%) of nonbleeding visible vessels. Seventy-seven patients (50.3%) were in shock before therapy. After therapy we obtained initial success in 147 cases (96.1%). Rebleeding episodes occurred in 23 patients (15.6%) within 1 month after therapy. Nineteen patients received a second therapy, and treatment in 15 of these cases (78.9%) was ultimately successful. Finally, treatment in 142 cases (92.8%) was ultimately successful. The duration of hospitalization was 6.3 +/- 0.4 days (mean +/- SEM). After discharge all patients were followed at the outpatient department for at least 1 month. Sixty-seven patients were followed endoscopically for at least 2 to 3 months after therapy. Fifty-six patients (83.6%) had a healed scar at the previous bleeding site 2 months after therapy, and 62 patients (92.5%) had a healed scar 3 months after therapy. We conclude that HP thermocoagulation is an ideal and reliable modality of therapeutic endoscopy in arrest of massive peptic ulcer hemorrhage. HP thermocoagulation may become the first choice of therapy for massive peptic ulcer bleeding in the near future.

Adolescent↗
PubMed1989

A tuberculostearic acid assay in the diagnosis of sputum smear-negative pulmonary tuberculosis. A prospective study of bronchoscopic aspirate and lavage specimens.

OBJECTIVE: To determine whether the detection of tuberculostearic acid (TBSA) in bronchial aspirate and bronchoalveolar lavage specimens is useful for the rapid diagnosis of active pulmonary tuberculosis in patients suspected of having the disease. SETTING: A pulmonary clinic in a teaching hospital. PATIENTS: Forty patients suspected of active pulmonary tuberculosis but who failed to produce sputum or whose sputum smears were negative for acid-fast bacilli on at least 3 occasions, 29 of whom were subsequently confirmed to have tuberculosis. A group of 13 patients who were having fiberoptic bronchoscopy for other reasons served as controls. INTERVENTION: All patients had fiberoptic bronchoscopy; bronchial aspirate, bronchoalveolar lavage, and sputum specimens were obtained when possible. MEASUREMENTS AND MAIN RESULTS: All specimens were examined microscopically for acid-fast bacilli, cultured for mycobacteria, and assayed for TBSA by gas chromatography and mass spectrometry with selected ion monitoring. Only 4 of the 29 patients with tuberculosis were diagnosed by direct microscopy compared with 26 by TBSA assay. In 2 patients who required surgical biopsy for conventional diagnosis, the TBSA test was positive. There were no false-positive TBSA results in the 13 controls, but 2 of 5 sputum specimens from the 11 test patients in whom tuberculosis was excluded were falsely positive, probably because of contamination with mouth flora. Because sputum can rarely be obtained from these patients and may give false-positive results, it is not a good specimen for TBSA assay. Sensitivities and specificities of the test for the other specimens were as follows: aspirate, 0.52 (CI, 0.32 to 0.71) and 1.00 (CI, 0.75 to 1.00); lavage, 0.68 (CI, 0.46 to 0.85) and 1.00 (CI, 0.84 to 1.00); aspirate and lavage combined, 0.79 (CI, 0.60 to 0.92) and 1.00 (CI, 0.86 to 1.00). CONCLUSIONS: The TBSA assay for bronchial aspirate and bronchoalveolar lavage fluid is useful for rapidly diagnosing "smear-negative" pulmonary tuberculosis. In these specimens it is highly specific and more sensitive than microscopy. This assay could be used to diagnose other mycobacterial infections, however, it cannot distinguish among species.

Bronchoalveolar Lavage Fluid↗
PubMed1989

Rapid HPLC assay of fluoroquinolones in clinical specimens.

A simple isocratic HPLC procedure was developed for the analysis of seven quinolones and their metabolites in clinical specimens. It is likely that this system can be used for the assay of many other quinolone compounds, but not for nalidixic acid and the ciprofloxacin metabolite sulpho-ciprofloxacin which appear to be adsorbed in the column. Sample preparation takes approximately 20 min, and HPLC analysis is completed within 15 min with a simple solvent system eluted on a reversed phase column. The procedure is rapid, sensitive and specific, and is a modification of an assay for chloramphenicol and beta-lactam antibiotics. This method is therefore particularly useful for clinical laboratories, since a single HPLC system can be used for assays of chloramphenicol, beta-lactams and quinolones.

4-Quinolones↗
PubMed1989

Excitatory synaptic responses in turtle cerebellar Purkinje cells.

1. Climbing fibre responses (CFRs) and parallel fibre responses (PFRs) in Purkinje cells have been analysed in intracellular recordings obtained at various levels from cell body to terminal dendrites in the turtle cerebellum in vitro. 2. With increasing stimulus intensity, the PFR recorded in distal dendrites displayed an early regenerative component which was graded at rest and at hyperpolarized membrane potentials, but was all-or-none at depolarized membrane potentials. 3. The all-or-none component had the same characteristics as Ca2+ spikes triggered by passing depolarizing current through the recording electrode. 4. The repolarizing phase of the PFR had a fast component enhanced by depolarization and diminished by hyperpolarization. 5. In the mid-molecular layer the PFR also included a plateau component which was increasingly prolonged by depolarization and abolished by hyperpolarization. 6. CFRs recorded in the soma had a plateau component, prolonged by local depolarization and abolished by local hyperpolarization. 7. The CFR in distal dendrites included a regenerative component. In some cells this component appeared in an all-or-none manner with local depolarization. In other cells it was smoothly graded with local polarization. 8. In mid-molecular records the CFR was prolonged by local depolarization and presumably electrotonically affected by the configuration of the response more distally and proximally in the cell. 9. It is concluded that excitatory synaptic responses in Purkinje cells include a regenerative Ca2+-mediated spike component in the spiny dendrites and a plateau component located in the proximal dendrites and/or the cell body. It is shown that both responses are modulated in configuration by the local membrane potential. In the spiny dendrites activation and inactivation of the transient hyperpolarizing potential appear to govern the Ca2+ influx during the CFR.

Action Potentials↗
PubMed1989

Pseudomonas peritonitis in CAPD patients: characteristics and outcome of treatment.

Twenty-five episodes of Pseudomonas peritonitis which occurred over a five-and-a-half-year period were reviewed. Pseudomonas peritonitis accounted for 25/516 (4.8%) of all episodes of peritonitis. Nine of the episodes were first infections in that the patient had not experienced peritonitis before. The rest were repeat peritonitis. There was no difference in any demographic factors between the first episodes and the repeat episodes except exit site infection which was more common among patients who had repeat infections. Overall cure rate of Pseudomonas peritonitis was 20/25 (80%). Five catheters had to be removed, all in patients who had to be transferred permanently to haemodialysis. In general, ceftazidime in combination with an aminoglycoside was an effective regimen. Oral ofloxacin was not useful despite in vitro sensitivity of the pathogen to the antibiotic.

Adult↗
PubMed1989

Climatic factors and peritonitis in CAPD patients.

From March 1983 to December 1987 the relation of the occurrence of all episodes of peritonitis in CAPD patients to climatic factors, such as temperature and relative humidity was examined. Altogether 389 episodes were recorded in 239 patients. Peritonitis due to Staphylococcus epidermidis, Gram-negative organisms and culture-negative episodes was most frequent during the hot months of the year, June to October. The occurrence of peritonitis due to Staphylococcus aureus was uniformly distributed throughout the year. Relative humidity did not seem to affect the frequency of peritonitis.

Climate↗
PubMed1988

Symptomatic anti-HBe positive chronic hepatitis B in Taiwan with special reference to persistent HBV replication and HDV superinfection.

Ninety-four patients, who were admitted with symptoms of liver disease and found to be positive for hepatitis B surface antigen and antibody to hepatitis B e antigen (anti-HBe), were examined for hepatitis B virus (HBV) DNA in serum and immunoglobulin antibody to hepatitis B core antigen and liver biopsies were stained for hepatic hepatitis B core antigen. Of 94 patients, 34 (36%) had evidence of HBV replication and 35 (37%) evidence of hepatitis D virus (HDV) superinfection. Most of the latter two groups of patients (greater than 70%) had evidence of chronic active hepatitis or active cirrhosis in their liver biopsies. The majority of these patients (greater than 80%) also had high levels of serum alanine aminotransferase (greater than 200 U/L) during the acute stage of their illness, and suffered from prolonged hepatic inflammation (greater than 1 year). Many of the patients (59%) also experienced frequent (1-6 episodes) relapsing exacerbations during a two-year follow-up period. Thus, persistent replication or reactivation of HBV and HDV superinfection were the two major causes of clinical exacerbations in anti-HBe-positive chronic HBV carriers in Taiwan, and also played an important role in the progression of their liver diseases and unfavorable outcomes.

Female↗
PubMed1988

Stimulus-induced extracellular pH transients in the in vitro turtle cerebellum.

In a number of CNS preparations, neuronal activation has been shown to result in a rapid extracellular alkaline transient, followed by a prolonged acid shift. The isolated turtle cerebellum was used to investigate the early alkaline transient. Double-barreled ion-sensitive microelectrodes for H+, K+ and tetramethylammonium were used to measure field potentials and extracellular ion and volume shifts in response to bipolar electrical stimulation of the parallel fibers. Transition from 15 mM HEPES to 35 mM HCO3- -buffered Ringer decreased the amplitude of the alkaline shift, presumably due to a marked increase in extracellular buffering power. In HEPES-buffered Ringer, repetitive stimulation produced alkaline shifts as large as 0.3-0.4 pH. Single shocks produced an alkaline shift of 0.006 +/- 0.0002 pH with a latency as short as 70 ms. Kynurenic acid (an excitatory amino acid antagonist), or Mn2+, blocked the alkaline shift and the postsynaptic component of the field potential. The alkaline shift was not blocked by the Na-H exchange inhibitor amiloride. The relationship between pHo and extracellular volume transients was studied using tetramethylammonium as an extracellular volume indicator. In nominally HCO3-free Ringer, stimulation at 5 Hz for 10 s caused a decrease in extracellular volume of 3.0 +/- 0.2 per cent. The volume transient was unaffected by 3 mM Mn2+, while the alkaline shift was completely abolished. The data for the alkaline shift are consistent with a channel-mediated transmembrane flux of proton equivalents. The size of the pH change and the underlying perturbation it represents, indicate that acid-base shifts may be a functionally important consequence of neuronal activity.

Action Potentials↗
PubMed1988

Effects of electric fields on transmembrane potential and excitability of turtle cerebellar Purkinje cells in vitro.

1. Transmembrane potential (TMP) responses of Purkinje cells (PCs) in isolated turtle cerebellum to externally applied quasi-steady-state electric fields aligned with the dendritic axis were continuously measured using simultaneous intracellular and extracellular recording. TMP was obtained by subtraction of extracellular voltage fields from intracellular potential recorded at the same depth in the cerebellum. 2. The applied field changed the TMP with the polarity and amplitude dependent on the location on the PC membrane. This response at a given location increased linearly with external field up to a threshold level, beyond which active responses appeared. 3. The basic effect on TMP consisted of depolarization in the half of the dendrite towards which the fields were directed, and hyperpolarization in the other half. A pooled TMP depth-profile shows a steady increase in polarization from the middle of the molecular layer towards each end. This profile correlates with that predicted from previously proposed cable models, giving them empirical support for the first time. 4. Active responses were triggered by the field-induced depolarization. Tetrodotoxin (TTX)-sensitive action potentials arose with the primary depolarization in the somatic region. Notched, Ca2+-dependent action potentials arose with primary depolarization in the distal and mid-dendritic regions. 5. A TTX-sensitive voltage plateau was triggered by TMP-depolarization in the proximal region. It in turn activated Na+-spike trains. The frequency of spiking was proportional to the external field. At around 160 spikes/s, the Na+ spikes inactivated, and the TMP level rose to a more depolarized plateau. This latter plateau was also TTX-sensitive. 6. During depolarization of the distal dendritic region, sometimes a Ca2+-dependent plateau was observed. It appears to be associated with a small conductance increase. 7. Field-induced hyperpolarization suppressed local spiking and voltage plateaux, but remote Ca2+ spikes with reduced amplitude appeared in recordings from the proximal region. Similarly, in the distal region, low-amplitude, remote Na+ spikes and a Na+ plateau were observed superimposed on the hyperpolarizing baseline. The Na+ plateau apparently did not contribute to shunting of membrane currents in the distal dendrite. 8. The phase characteristics of the action potentials correlate with the modulation pattern noted in our extracellular study (Chan & Nicholson, 1986). Thus, the extracellular units ("giant spikes") were probably Na+ spikes activated in the soma and spread distally. Occasionally Ca2+ spikes, with a higher threshold, might also be activated to give dual-phase response.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Diagnosis of nasopharyngeal tuberculosis by detection of tuberculostearic acid in formalin fixed, paraffin wax embedded tissue biopsy specimens.

The use of gas chromatography and mass spectrometry with selected ion monitoring detected tuberculostearic acid (TBSA) in 10 of 12 formalin fixed, paraffin wax embedded nasopharyngeal and head and neck biopsy specimens from patients with confirmed tuberculosis and carcinoma, and in one of 50 control specimens (giving a sensitivity of 83% and a specificity of 98%). The two false negative cases had very small tissue fragments and the patient with a false positive result may have had pulmonary tuberculosis. Tuberculostearic acid (TBSA) was also detected in nine of 16 specimens from the head and neck region with non-caseating granulomas suspected, but not confirmed, to be tuberculosis. It is concluded that nasopharyngeal tuberculosis is relatively common in Hong Kong and should be considered when biopsy specimens show granulomas. The detection of TBSA in tissue biopsy specimens is a useful, rapid method for the diagnosis of tuberculosis and other mycobacterial infections, and can be conveniently performed within two days on formalin fixed and paraffin wax embedded material.

Granuloma↗
PubMed1988

Comparison of enzyme- and radio-immunoassay kits to detect hepatitis B surface antibody response among hepatitis B vaccinees.

A total of 288 of sera was obtained from 96 hepatitis B vaccinees to test antibody to hepatitis B surface antigen (anti-HBs) by enzyme immunoassay (EIA) and radioimmunoassay (RIA), respectively. An anti-HBs titer greater than 10 mIU/mL is required for immunity; 172 (59.7%) were positive by EIA and 173 (60.1%) were positive by RIA. A correlation study of anti-HBs titers tested by these two methods showed a correlation coefficient r = 0.889 (n = 162, p less than 0.001). Of 173 serum specimens whose anti-HBs were positive by RIA, 10 were negative by EIA; those 10 had had anti-HBs titers between 11 to 20 mIU/mL by RIA. Among 172 serum specimens whose anti-HBs were positive by EIA, 9 were negative by RIA; 3 of those were between 21 to 70 mIU/mL, and 6 were between 11 to 20 mIU/mL by EIA. Of the 96 vaccinees, following first dose of hepatitis B vaccination their anti-HBs response rates were found to be 20.8% by EIA and 17.7% by RIA. Following second and third vaccinations, their anti-HBs response rates were 65.6% and 92.7% by EIA, and 71.9% and 90.6% by RIA, respectively. Thus, EIA correlates well with RIA for anti-HBs testing especially when its titers are greater than 70 mIU/ml.

Adolescent↗
PubMed1987

Diagnosis of tuberculous meningitis by detection of tuberculostearic acid in cerebrospinal fluid.

Tuberculostearic acid, a structural component of Mycobacterium tuberculosis, was identified by gas chromatography/mass spectrometry with selected ion monitoring in cerebrospinal fluid (CSF) from 13 patients with proven and 8 out of 9 patients with suspected tuberculous meningitis; the negative result was in a patient whose symptoms and CSF abnormalities may have been due to systemic lupus erythematosus. Tuberculostearic acid was found in the CSF of only 1 patient out of 87 with non-tuberculous meningitis or non-infectious disorders; the single false-positive result was probably caused by intrathecal treatment with amikacin. Other aminoglycosides and antituberculous drugs did not interfere with the assay. In serial CSF samples from patients with tuberculous meningitis tuberculostearic acid was still present after 8 months of continuous supervised chemotherapy. Detection of tuberculostearic acid in CSF is a rapid, sensitive, and specific test for tuberculous meningitis, and can be used for retrospective diagnosis in patients who have been started on therapy.

Adult↗
PubMed1987

Diagnosis of pulmonary tuberculosis by detection of tuberculostearic acid in sputum by using gas chromatography-mass spectrometry with selected ion monitoring.

Tuberculostearic acid [(R)-10-methyloctadecanoic acid (TBSA)] is a structural component of mycobacteria, and its detection in appropriate clinical specimens has potential application as a rapid screening method for the presence of Mycobacterium tuberculosis and other mycobacteria. We used the highly sensitive technique of gas chromatography-mass spectrometry (GC-MS) combined with selected ion monitoring (SIM) of m/e 312 and m/e 167 for detecting TBSA in 405 clinical sputum specimens collected in Hong Kong, where tuberculosis is still common. TBSA was detected in 39 M. tuberculosis smear-positive, culture-positive specimens; 63 of 66 smear-negative, culture-positive specimens; and 1 of 300 smear-negative, culture-negative specimens. Thus, for screening of sputa from individuals with suspected pulmonary tuberculosis, the detection of TBSA by GC-MS/SIM is highly specific and more sensitive than conventional microscopy and more rapid but slightly less sensitive than conventional culture methods.

Gas Chromatography-Mass Spectrometry↗
PubMed1986

Rapid high performance liquid chromatographic assay of cephalosporins in biological fluids.

A simple isocratic HPLC method is described for the rapid analysis of cephalosporins in body fluids. Sample preparation by protein precipitation takes only five minutes; HPLC analysis is completed within two to ten minutes, using one of two simple solvent mixtures eluted on a single C18 reversed phase column. Nine cephalosporins and nine types of body fluid were formally analysed, but the system was also found to be suitable for the assay of benzyl penicillin, ampicillin, cloxacillin, carbenicillin and chloramphenicol. It is likely that this method, with only minor modifications, would be suitable for the analysis of most beta-lactam antibiotics in most clinical specimens. The method is therefore particularly recommended for use in clinical laboratories.

Body Fluids↗
PubMed1986

Modulation by applied electric fields of Purkinje and stellate cell activity in the isolated turtle cerebellum.

Quasi steady-state electric fields were applied across the isolated turtle cerebellum to study the relationship between applied field, neuronal morphology and the modulation of the neuronal spike firing pattern. Spiking elements were identified electrophysiologically using extracellular recording methods and by subsequent horseradish peroxidase injection, which revealed their dendritic morphology and orientation. The electric field was precisely defined by measuring the voltage gradients induced in the cerebellum by 40 s constant-current pulses. The field was constant in the vertical (dorso-ventral) axis and zero in the horizontal plane, in agreement with theory. Neurones were modulated by applying a sinusoidal field at frequencies between 0.05 and 1.0 Hz. Modulated cells exhibited an increase in firing frequency and fell into one of four classes, depending on the direction of the field that produced the modulation. Thus neurones were excited by: ventricle-directed fields (V modulation), pia-directed fields (P modulation), both of the above (V/P modulation) or showed no consistent modulation (non-modulation). Most Purkinje somata and primary dendrites (nineteen out of twenty-eight) and most Purkinje dendrites (eighteen out of thirty), were V modulated with maximum rate proportional to the peak field intensity. The dendrites of these cells were consistently oriented toward the pia. Among the stellate cells, the lower molecular layer stellates, with dendrites extending predominantly towards the pia, were mostly (nineteen out of thirty-two) V modulated. The mid-molecular layer stellates, which showed much variability in dendritic orientation, were distributed among all four of the modulation classes. The upper molecular layer stellates, with a mostly horizontal dendritic alignment, were mainly (nine out of sixteen) non-modulated. All groups of spiking elements showed a correlation between patterns of modulation by applied fields and dendritic orientation, which suggests the degree of differential polarization of the extended cable elements of the neurone by the applied field as the basic mechanism for field-induced excitation or inhibition. The threshold for modulation among all neurones was 15-20 mV/mm, which is similar to the fields that modulate other nervous tissues. This suggests that many neurones can be modulated by fields of the order of 10-20 mV/mm.

Action Potentials↗
PubMed1985

Benzodiazepine receptor photoaffinity labeling: correlation of function with binding.

Exhaustive photoaffinity coupling of flunitrazepam to living spinal cord neurons reduced the capacity of benzodiazepines to potentiate the electrophysiologically measured GABA response. In qualitative agreement with reversible binding data the dose-response curve for enhancement of the GABA response by benzodiazepines was shifted to the right, indicating that the remaining reversible benzodiazepine binding sites have lower affinity for benzodiazepines. Photoaffinity labeling did not reduce inhibition of the GABA response by beta-carbolines and there was only a small decrease in beta-carboline binding. In both control and photoaffinity-labeled cultures, the inhibitory effect of beta-carbolines on the GABA response was reversed in the presence of excess benzodiazepine. The results indicate that the effects of photoaffinity labeling are confined to the BZD recognition site, and that coupling between benzodiazepine receptors and GABA receptors remains intact.

Affinity Labels↗
PubMed1985

Location of membrane conductance changes by analysis of the input impedance of neurons. II. Implementation.

Mathematical modeling has shown that it should be possible to determine the electrotonic location of membrane conductance changes in single neurons by analysis of the associated changes in the magnitude of the alternating-current (AC) input impedance. The form of the plot of change in the magnitude of the input impedance as a function of frequency (delta [Zn(f)]) should differ for changes in membrane conductance located at different electrotonic distances from the recording/current-injection site. Due to the axial resistance and the membrane capacitance, the higher frequencies are attenuated with distance to a greater degree than are the lower frequencies. Thus delta [Zn(f)] should drop to zero more rapidly with increasing frequency for distal than for proximal conductance changes. For distal changes in conductance, the sign of the change in the magnitude of the input impedance can even reverse in the higher frequency range, so that increases in conductance would produce increases in impedance. This effect may explain the paradoxical increases in impedance at 100 Hz reported for motor neuron inhibitory postsynaptic potentials. Sine-wave impedance measurements were made in single embryonic chick spinal neurons in tissue culture, and gamma-aminobutyric acid (GABA) was iontophoretically applied alternately to the soma and to a neurite at a measured distance from the soma. The impedance changes produced by the GABA-induced conductance changes were consistent with the expectations from the mathematical modeling, but the results suggest that the axial resistance of the neurites must be quite high in some cases. Distortions due to microelectrode capacitance and stray capacitances in the input stage of single-electrode bridge amplifiers can make sine-wave impedance measurements impossible. This difficulty was eliminated by modifications to the capacity compensation circuit of an active bridge amplifier. Noise and distortion of several other types can also introduce serious errors. Methods for minimizing such problems are discussed. In spite of its limitations, this method can be of great practical value, because it can give the electrotonic location of spontaneously occurring membrane conductance changes in single neurons even when unitary synaptic potentials cannot be resolved. These methods are currently being applied to hippocampal pyramidal cells in vivo to locate conductance changes during the electroencephalogram (EEG) theta-rhythm in rats. In such laminated structures, the determination of the anatomical source of a group of active synapses can be aided by location of the resultant membrane conductance changes.

Animals↗